1. Field of the Invention
The present invention relates to a magnetic sensor, a magnetic head and a magnetic recording/reading apparatus.
2. Background Art
In the field of magnetic recording/reading apparatus, an increase in recording density at an almost 100% annual rate is required. Also a magnetic recording/reading head provided in this magnetic recording/reading apparatus is required to provide higher performance in the two characteristics of recording and reading.
For a magnetic recording/reading head, it is important to solve the three technical problems of (1) an improvement of techniques for increasing sensitivity, (2) an improvement of techniques for narrowing the track width, and (3) techniques for narrowing the read gap distance.
For the problem (1) above, this high recording density design has been coped with by using the anisotropic magnetoresistive (AMR) effect for recording densities of 1 to 10 (Gb/in.2), the giant magnetoresistive (GMR) effect, which ensures higher sensitivity, for high recording densities of 10 to 30 (Gb/in.2), and the advanced GMR effect called a specular GMR effect or a nano-oxide layer GMR effect aimed at an increase in output by the multi-reflection effect of electron spins, in which a (mirror reflection) insulator oxide layer of high electron reflectivity and the like are sandwiched between interlayers of a GMR structure, for recording densities of 20 to 70 (Gb/in.2).
For a magnetic head using the GMR effect, a structure called a spin-valve is disclosed in the JP Patent Publication (Kokai) No. 4-358310 (Literature 1). This magnetic head is constituted by a pinned layer formed from a magnetic layer whose magnetization is pinned by an antiferromagnetic layer in a specific direction, a nonmagnetic thin film laminated in this pinned layer, and a free layer formed from a ferromagnetic layer laminated via this nonmagnetic thin film, and has a magnetoresistive device whose electrical resistance changes according to a relative angle of magnetization of the pinned layer and the free layer.
Furthermore, in the JP Patent Publication (Kokai) No. 2000-137906 (Literature 2), the JP Patent Publication (Kokai) No. 2001-168414 (Literature 3) and the JP Patent Publication (Kokai) No. 2001-230471 (Literature 4) is described a structure with an improved MR (magnetoresistive) ratio in a CIP-GMR (current-in-plane GMR) element, in which an oxide layer is inserted into at least either of the free layer side and the pinned layer side and a multi-reflection of electrons is generated by utilizing the mirror reflection of the oxide, thereby to improve the magnetoresistive ratio. In the JP Patent Publication (Kokai) No. 2002-190630 (Literature 5) there is also shown a CIP-GMR structure in which a half-metal layer is interposed between a free layer and an intermediate layer or between an intermediate layer and a pinned layer.
At present, a higher reading method is required due to further progress in high sensitivity design. At 70 to 150 (Gb/in.2), the tunneling magnetoresistive (TMR) effect with a very high MR ratio is effective from the standpoint of an improvement of sensitivity. And it might be thought that for ultrahigh recording densities exceeding 150 (Gb/in.2), the GMR (CPP-GMR) effect and the like of a method which involves causing a detection current to flow in a direction perpendicular to the film surface become mainstream by making the most of the advantage that the device impedance is small. TMR is released to the public as a basic technique in the JP Patent Publication (Kokai) No. 3-154217 (Literature 6) and also in the JP Patent Publication (Kokai) No. 10-91925 (Literature 7) etc.
In the case of CIP-GMR, the insulation between a device and a shield poses a problem when the shield gap distance is shortened to cope with high track recording density design. In contrast to this, in the case of CPP-GMR, the insulation characteristics do not pose an important problem and the effects of a thermal device breakdown by static voltage and current and a change to nonlinearity by a magnetic field seem to be small. Although many CPP-GMR structures have been reported, representative ones are described in the JP Patent Publication (Kohyo) No. 11-509956 (Literature 7) and the JP Patent Publication (Kokai) No. 7-221363 (Literature 8).    [Literature 9] Electrical detection of spin precession in a metallic mesoscopic spin valve, F. J. Jedema et al., NATURE, VOL 416, pp 713-716, 18 Apr. 2002    [Literature 10] Physical Review B, VOLUME 59, NUMBER 1, pp 93-96    [Literature 11] Physical Review B, VOLUME 65, 054401, pp 1-17    [Literature 12] S. Q. Liu et al., APPLIED PHYSICS LETTERS, VOLUME 76, NUMBER 19 (2000), pp 2749-2751